Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 230306
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1006 PM EST MON DEC 22 2014

.SYNOPSIS...
A MOIST AIRMASS WILL REMAIN ATOP THE REGION BEFORE A COLD FRONT
CROSSES BY WEDNESDAY NIGHT. DRY HIGH PRESSURE WILL ARRIVE FOR
CHRISTMAS DAY AND LINGER INTO FRIDAY. ANOTHER COLD FRONT WILL CROSS
THE AREA ON SATURDAY...FOLLOWED BY HIGH PRESSURE ON SUNDAY.

&&

.NEAR TERM /THROUGH TUESDAY/...
EVENING UPDATE...MADE MINOR TWEAKS TO POPS AND TEMPS/TDS. RADAR
SHOWS DEEPER MOISTURE ASSOCIATED WITH ULVL VORT ENERGY PASSING
ACROSS THE ERN ZONES. AFTER THIS MOVES EAST...LIGHT RAIN AND AREAS
OF DRIZZLE WILL REMAIN ACROSS THE CWFA THROUGH THE OVERNIGHT. PATCHY
OR AREAS OF DENSE FG ARE POSSIBLE AROUND SUNRISE WITH SATURATED
LLVLS...ALTHOUGH SFC WINDS MAY REMAIN STRONG ENUF TO OFFSET THIS
SCENARIO.

AS OF 635 PM...LIGHT RAIN SHIELD IS MOVING IN A BIT FASTER THAN
PROGGED ACROSS THE SW/RN ZONES...SO POPS WERE ADJ UP INTO THE
LIKELY/CAT RANGE. LOW END QPF AMOUNTS STILL LOOK GOOD. TEMPS AND
TD/S REMAINING NEARLY STEADY STATE IN HIGHLY MOIST
ENVIRONMENT...THUS ONLY MINOR TWEAKS NEEDED TO THESE GRIDS.

AS OF 225 PM...COLD TEMPS...LOW CLOUDS AND PATCHY DRIZZLE WILL
CONTINUE THRU THE AFTERNOON...EXCEPT ALL BUT THE TN BORDER COUNTIES
WHERE BREAKS IN THE CLOUDS HAVE LEAD TO RELATIVELY WARM TEMPS.
PATCHY RAIN BEGINNING TO SPREAD BACK INTO THE SRN TIER OF THE CWFA
AND THIS TREND WILL CONTINUE THRU THE AFTERNOON...WITH SOME SLOW
NORTHERLY MOVEMENT OF THE PRECIP.

A SERIES OF SHORT WAVES WILL MOVE ACROSS THE AREA IN THE SWLY FLOW
AHEAD OF A DEEPENING CENTRAL CONUS TROF TONIGHT AND TUESDAY. AT THE
SFC...CAD REGIME WILL REMAIN IN PLACE THRU THE PERIOD AS WELL
KEEPING COPIOUS AMOUNTS OF LOW LEVEL MOISTURE ACROSS THE AREA AND
NELY SFC FLOW...EXCEPT ACROSS THE MTNS WHERE SLY FLOW PREVAILS. THE
LOW LEVEL FLOW WILL REMAIN SLY AS WELL...AND STRENGTHEN TONIGHT
INCREASING ISENTROPIC UPGLIDE ACROSS THE AREA. THEREFORE...RAIN SHUD
RETURN ALONG WITH THE CONTINUING DRIZZLE THRU THE NITE. EXPECT LOW
CLOUDS AND AREAS OF FOG TO CONTINUE OR REDEVELOP AS WELL. CANNOT
RULE OUT SOME PATCHY DENSE FOG TOWARD DAYBREAK...BUT LOCATION NOT
CERTAIN ENUF TO INCLUDE IN THE FCST ATTM. LOWS WILL BE IN THE 30S
FOR ALL BUT THE HIGHER ELEVATIONS OF THE SWRN MTNS AND TN BORDER
COUNTIES WHERE THEY ARE OUTSIDE OF THE CAD DOME AND TAP INTO THE
WARMING H85 TEMPS. THIS WILL ALSO HELP KEEP PRECIP ALL LIQUID.

THERE MAY BE A BRIEF BREAK IN THE BETTER LIFT TUE MORNING...BUT IT
RETURNS THRU THE DAY...ALONG WITH DEEPER MOISTURE AND SOME UPPER
DIVERGENCE AS A JET STREAK MOVES NORTH INTO THE AREA. EXPECT RAIN
AND DRIZZLE TO BECOME WIDESPREAD BY AFTERNOON...ALTHOUGH AREAS OF
DRIZZLE WILL LIKELY CONTINUE EVEN WHERE RAIN DIMINISHES. EXPECT
ANOTHER COOL DAY UNDER THE CAD. HOWEVER...WOULD NOT BE SURPRISED IF
TEMPS WARM A FEW DEGREES ABOVE THE MONDAY READINGS AS THE PARENT
HIGH IS SHUNTED EASTWARD AND CAD TAKES ON MORE OF AN IN-SITU
PATTERN. THE TN BORDER COUNTIES WILL ONCE AGAIN BE MUCH WARMER THAN
AREAS UNDER THE CAD.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AT 200 PM EST MONDAY..12Z MODEL RUNS INDICATE THAT SOME SEMBLANCE OF
A WEDGE WILL REMAIN THROUGH MOST IF NOT ALL OF TUE NIGHT. THE NAM
DOES SUGGEST THAT PERHAPS THE SOUTHERN UPSTATE MAY GET UNCOVERED BY
12Z WED. THE UPSHOT FOR TUE NIGHT IS THAT ISENTROPIC LIFT WILL
CONTINUE OVER THE WEDGE WITH WIDESPREAD LIGHT TO EVEN MODERATE RAIN.
BEST RAINFALL RATES ARE EXPECTED TO BE OVER THE WESTERN UPSTATE...NE
GA MOUNTAINS AND THE WESTERN ESCARPMENT WHERE BEST FORCING/UPSLOPE
FLOW WILL BECOME ESTABLISHED. RAINFALL IN THOSE AREAS IS LIKELY TO
BE UPWARDS OF AN INCH. ON WED...THE CONSENSUS IS THAT THE REMAINDER
OF THE WEDGE WILL GRADUALLY BE UNCOVERED...BUT AS USUAL IT COULD
LINGER WELL INTO THE AFTERNOON FROM THE CENTRAL UPSTATE EASTWARD.
RAIN/DRIZZLE WILL BECOME SHOWERY AS WEDGE DISSIPATES. THE NEXT ISSUE
IS THE COLD FRONT THAT WILL TRANSLATE ACROSS THE AREA FROM THE WEST
AS LOW PRESSURE MOVES FROM CENTRAL TN TO THE LOWER GREAT LAKES ON
WED. THE 12Z MODELS ARE TRENDING SLOWER WITH THE FRONTAL PASSAGE...
WITH THE NAM THE SLOWEST OF THE OPERATIONAL RUNS....A GOOD 6 HOURS
SLOWER THAN THE GLOBAL MODELS. THE 09Z SREF SUPPORTS THE SLOWER NAM.
IN REGARD TO TIMING WILL USE A CONSENSUS APPROACH WHICH WILL MOVE
THE FRONT INTO WESTERN SECTIONS DURING WED AFTERNOON AND THEN ACROSS
THE REMAINDER OF THE AREA LATE WED AFTERNOON/EVENING. THE MAIN
CONCERN WITH THE FRONTAL PASSAGE WILL BE THE THREAT FOR SOME SORT OF
QLCS EVENT. ALL THE MODELS SHOW SOME LOW END CAPE UPWARDS OF 200
J/KG AHEAD OF THE FRONT. SHEAR/HELICITY IS ADEQUATE ALTHOUGH NOT
THROUGH THE ROOF BUT FORECAST SHERB VALUES GENERALLY <1.  ALSO...THE
UPPER FORCING IS NOT COINCIDENT WITH THE FRONT. THE UPPER TROUGH IS
FORECAST TO TRAIL THE SURFACE FRONT WITH THE MAIN UPPER FORCING
GOING WELL NORTH OF THE REGION. HENCE...CHANCES FOR SEVERE
CONVECTION APPEAR ON THE LOW END. THE CIPS ANALOG DOES MAKE ME PAUSE
AS IT PAINTS A 30% AREA OF TOP ANALOGS PRODUCING AT LEAST 1 SEVERE
EVENT ACROSS THE PIEDMONTS OF NE GA...SC AND NC. SPC KEEPS THE
MENTION OF SEVERE EAST OF THE AREA...SO BOTTOM LINE IS THAT WE WILL
NOT NOT MENTION THE THREAT OF SEVERE IN THE HWO. DRYER AIR AND
DOWNSLOPING WINDS WILL FINALLY SCOUR CLOUDS OUT EAST OF THE
MOUNTAINS WED NIGHT WITH PERHAPS A PERIOD OF SOME NW FLOW SNOW/RAIN
SHOWERS EARLY CHRISTMAS IN THE MOUNTAINS.

IN REGARD TO HYDRO...I HAVE HEFTY QPF IN MY FORECAST GRIDS WITH
STORM TOTAL RAINFALL AROUND 2.5 INCHES OVER NE GA...WESTERN UPSTATE
AND THE WESTERN ESCARPMENT. HOWEVER...ANTECEDENT CONDITIONS ARE
BENIGN SO DO NOT ANTICIPATE ANY SIGNIFICANT HYDRO CONCERNS.

TEMPERATURES WILL BE A CHALLENGE AS A NON-DIURNAL TREND WILL OCCUR
TUE NIGHT WHERE THE WEDGE ERODES. THIS WOULD MOST LIKELY BE ACROSS
THE SOUTHERN PERIPHEREY OF THE FORECAST AREA. TEMPS ON WED SHOULD
SURGE WELL INTO THE 60S AS THE WEDGE DISSIPATES. COOLER TEMPS WILL
THEN OCCUR WED NIGHT WITH MAX TEMPS THU NEAR CLIMO.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 200 PM MONDAY...HIGH PRESSURE OVER THE SRN ATLANTIC REGION WILL
MAKE FOR SETTLED CONDITIONS IN OUR AREA THU NIGHT THRU EARLY
SAT...BEFORE THE HIGH IS FORCED OFFSHORE BY A LONGWAVE TROUGH DIGGING
INTO THE CENTRAL CONUS. GLOBAL MODELS HAVE DELAYED ARRIVAL OF THE
COLD FRONT ON THE LEADING EDGE OF THE TROUGH...NOW SUGGESTING THE
FRONT WILL CROSS THE MTNS DURING THE DAY SAT AT THE EARLIEST.

THE GFS HAS MAINTAINED CONSISTENCY WITH EARLIER RUNS...DEAMPLIFYING
THE TROUGH OVER THE WEEKEND AND ALLOWING DRY HIGH PRESSURE TO FILL IN
ACRS THE SOUTHEAST IN ITS WAKE. EC AND NOW THE OPNL CMC-GEM SHOW A
SIMILAR EVOLUTION ALBEIT MARKEDLY DIFFERENT FROM THE GFS. THEY DEPICT
A SHORTWAVE SHEARING OFF THE TROUGH OVER THE SRN PLAINS SATURDAY
WHICH INDUCES GULF CYCLOGENESIS AND MAKES FOR A WET SUNDAY OVER OUR
CWFA. THIS IS NOT INDICATED BY ANY 22/06Z GEFS MEMBERS AND ONLY A
COUPLE OF THE 22/12Z GEM ENSEMBLE MEMBERS. NOTING HOW DIFFERENT THE
EC/CMC SOLUTION IS FROM EARLIER RUNS IT APPEARS WISE TO DISCOUNT IT
TO SOME DEGREE. LOOKING A BIT FURTHER FORWARD...GFS DOES FEATURE ITS
OWN DIFFERENCES BY LATE MONDAY AS IT SPINS UP A NEW GULF LOW AT THAT
TIME AND BEGINS TO SPREAD PRECIP NWD THRU GA/SC. CONFIDENCE IN THE
FCST IS NOT VERY HIGH BEYOND SATURDAY.

TEMPS SHOULD TREND UPWARD THRU SUNDAY...WITH MINS ENDING UP A COUPLE
DEGREES ABOVE CLIMO AND MAXES 5-7 ABOVE CLIMO. SLIGHTLY COOLER TEMPS
RETURN FOR MONDAY WITH HIGH PRESSURE JUST NORTH OF THE REGION.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
DDHHMM
WRKTAF

AT KCLT...LLVL MOISTURE FEED REMAINS CONSTANT OVER SFC WEDGE WITH
DEEPER FORCED MOISTURE MOVING INTO AREA WITHIN THE NEXT FEW HRS.
CIGS HOLDING STEADY IN THE LIFR RANGE AND WILL EXPECT THESE TO
PERSIST THROUGHOUT THE TAF PERIOD. INCOMING -RA COULD SCOUR OUT VSBY
A BIT INTO THE 3-4SM RANGE...WITH A DROP BACK TO 1SM OR LESS AFT
09Z THRU DAYBREAK. DENSE FG IS POSSIBLE ARND DAYBREAK AS WELL.
ANOTHER ROUND OF MODERATE RAIN MOVES IN NEAR THE END OF THE
TAF PERIOD WITH VSBYS IMPROVING SOMEWHAT. WINDS REMAIN LOCKED IN
NE/LY IN CAD FLOW.

ELSEWHERE...SIMILAR CONDS AT ALL SITES THROUGH THE TAF PERIOD. LOW
IFR TO LIFR CIGS ALIGNED IN LLVL CAD MOISTURE WILL PERSIST
THROUGH THE TAF PERIOD...WHILE -DZ AND -RA AFFECT THE TERMINALS.
VSBYS WILL WAVER BACK AND FORTH BETWEEN 1-5SM WITH THE POTENTIAL FOR
DENSE FG AROUND DAYBREAK. WINDS REMAIN ALIGNED NE/LY NON/MTNS AND
S/LY DOWN VALLEY FLOW AT KAVL.

OUTLOOK...DEEP MOISTURE CONTINUES THROUGH TUESDAY NIGHT AHEAD OF THE
NEXT APPROACHING COLD FRONT. LOW RESTRICTIONS AND WIDESPREAD RAIN
SHOWERS ARE EXPECTED. A COLD FRONT WILL CROSS THE REGION FROM THE
WEST ON WED. DRY HIGH PRESSURE WILL RETURN THROUGH LATE WEEK.

CONFIDENCE TABLE...

            03-09Z        09-15Z        15-21Z        21-00Z
KCLT       MED   71%     MED   75%     MED   75%     HIGH  90%
KGSP       MED   60%     MED   75%     MED   72%     MED   76%
KAVL       MED   73%     HIGH  88%     MED   66%     HIGH  90%
KHKY       MED   66%     MED   75%     MED   77%     HIGH  90%
KGMU       LOW   55%     MED   75%     MED   72%     MED   76%
KAND       MED   66%     MED   75%     MED   72%     MED   70%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...CSH
NEAR TERM...RWH/SBK
SHORT TERM...LG
LONG TERM...WIMBERLEY
AVIATION...SBK



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